In many prior arts, such as U.S. Pat. Nos. 1,501,212, 1,792,338, 2,582,591, 3,535,959, 3,817,128, 4,106,372, and 5,152,198, the adjustable spanners capable of adjusting size of an opening rapidly are disclosed. However all the structures of the spanners are too completed to be made. The operation is unsteady so as to affect the error of the opening of the spanner. This is because in the forging process, the error cannot be avoided, generally, the error is about 0.3 mm to 0.8 mm. This will induce that the grooves in the head of the handle cannot be controlled precisely so that two pressible units are not symmetrical to the center of the head of the handle. Further the heat process will cause the deformation of the parts of the handle so that when a cover is locked to a shoulder, the two sides will curl to affect the smoothness in the pressing operation.
Although CNC lathe can be used to improve the above mentioned defects from forging and heat processing, the CNC process is too expensive. It is not economic to the manufacturing of the spanner.